media: v4l2-tpg: show either Y'CbCr or HSV encoding

When logging the current TPG state detect if we are generating
a Y'CbCr or HSV pattern and report one or the other instead of
both, which is confusing.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>